1. Field of the Invention
This invention relates to rotary actuators, particularly compound rotary actuators in which the final output member can be rotated in two planes perpendicular to one another. A specific application is rotary actuators of the compound motion type used in conjunction with an industrial robot for handling worpieces or with a boom supported rock drill apparatus for positioning the rock drill on the vehicle.
2. Description of the Prior Art
Rotary actuators in their most simple form frequently employ a piston powered rack which is reciprocally mounted in a cylinder and which meshes with a pinion secured to an output shaft which is rotatably mounted in a second cylinder or external output shaft housing. Conventionally, the rack enclosing cylinder is threaded into the output shaft housing. This provides a very easy to manufacture actuator but has disadvantages. The threaded connection between the rack enclosing cylinder and the output shaft housing is by virtue of its threads unable to transmit torque in two directions.
Mobile rock drilling apparatus have the requirement that the drilling head mounted on the end of an articulated boom be rotatable in two planes of motion at right angles to one another. That is, the rock drill head must be rotated, for example, in a horizontal plane and also rotated or flipped over in a vertical plane. Even more important applications for compound rotary actuators are workpiece handling devices or robots for remotely manipulating objects. Conventionally, this compound rotation is provided by plural cylinder and piston actuators such as shown in U.S. Pat. No. 3,020,012. These cylinder piston actuators are expensive to maintain, cumbersome to utilize and are expensive to manufacture.